be doing是谓语吗

是。be+doing这个部分，如在句子里I am doing my homework.主语是I谓语是am doing 宾语是my homework。be+doing 是系动词加现在分词构成进行时态，但doing是动名词或者现在分词是不能单独做谓语的，所以是非谓语动词。

表达将来时的几种结构：
1.be going to do
表示最近打算进行的事，具有一定的目的性和计划性。（这种安排既有可能是主语做出的,也有可能是别人安排的。）
We are going to have a meeting tomorrow.
表示即将要发生的事情，不可避免要发生的事情。（多用于表天气）
It's getting cloudy. It is going to rain.
2.be to do
表示按计划要发生的事，一般认为，这种计划是双方约定的，而be going to do所指的安排不一定是双方约定的。
We are going to meet them at the north of the bridge, because it is the only road they can follow. 我们打算去桥的北边堵他们，因为那是他们的必经之路.
We are to meet each other with them at the north end of the bridge. 双方约定好要在桥的北边见面.

be to do 还有很多情态用法，be going to do没有以下用法.
You are to wash your hands before every meal.表需要=need
As Warrent's parents,you are to set a good example to him.（表责任，义务，相当于must should） Are we to clean the corridor,Mrs Dell? （表征求意见=shall）
The temperature is to drop soon.（表示可能性）
Would she get cross if I were to sail into her of lying?（表假设）